Traditional path diversity schemes take advantage of diversity associated with signals transmitted over multiple paths, to improve the performance of a communication system. Information originating from a single data source can be intentionally or unintentionally propagated over multiple paths before arriving at a destination receiver. Typically, the propagation of a signal over the multiple paths causes different “versions” of the signal to arrive at the receiver at different time offsets, and at approximately the same frequency. The multiple paths may occur due to signal reflections, may occur due to delays attributable to one or more signal processing devices, such as repeaters, interposed between the transmitter and receiver, or due to some combination of physical paths and delays through signal processing devices. The difference in time of arrival associated with the different signal paths increases as the physical distances traversed by multiple signal paths increase. The receiver may be able to benefit from the existence of such multiple paths, or path diversity, if the receiver is able to properly process each of the delayed versions of the transmitted signal.
Techniques that take advantage of path diversity are well known and practical to implement for systems in which the maximum difference in time of arrival is on the order of 10 symbol intervals or less. Specifically, the optimum demodulator of a multipath signal is the well known Maximum Likelihood Sequence Estimation, which is commonly implemented using the Viterbi Algorithm. This approach is practical when the difference in the path delays between the paths is a relatively small number of symbols, e.g., <≈10, but is unpractical for scenarios such as that depicted in FIG. 1 where the differential path delay can be thousands of symbols in duration. Another approach is the classic RAKE receiver, which is also well known to those of ordinary skill in the art. The RAKE receiver provides a good approximation to the optimal receiver when the signal to noise ratio (SNR) is very low, e.g., <≈−6 dB. For this reason, the RAKE receiver is commonly used with spread spectrum signals, such as code division multiple access (CDMA) signals. But for higher SNR environments that are common in non-spread spectrum applications, the RAKE receiver is ineffective. Thus, traditional path diversity schemes have been limited in their application.
For example, for communication systems involving non spread spectrum signals transmitted over multiple paths that have significant differences in their time of arrival, such traditional path diversity schemes are inadequate. These include systems that handle signals sent from a single transmitter over multiple paths, as well as systems that handle signals sent from distinct transmitters over multiple paths. Thus, there is an important need for techniques that allow generating and processing of multiple path diversity, co-frequency signals, especially in cases where the delay spread between the diversity paths is large relative to the symbol period.